Don’t play with fire

Arc flash can seriously injure workers. Learn the basics of NFPA 70E and protect your workers from arc flash and flash fire.

by Paul Markgraff

Imagine working on a jobsite where the ambient temperature exceeds 35,000 F, nearly four times the temperature of the surface of the sun. This place is so inhospitable, sound waves can reach 141.5 decibels and air pressure can climb to 2,160 lbs. per sq. ft.

This jobsite does not exist on some other planet; rather, it can be found every day here on earth.
These are the characteristics of arc flash, a short circuit that occurs through the air when a worker accidentally makes contact with energized conductors or circuits.

The statistics are unsettling:
One person is fatally electrocuted in the workplace every day.
Electrocutions are the fourth leading cause of traumatic occupational fatalities.
More than 2,000 workers are sent to burn centers each year with electrical burns.
An average of 4,000 non-disabling and 3,600 disabling electrical contact injuries in the workplace occur every year in the U.S.

The basics on NFPA 70E
The National Fire Protection Agency (NFPA) published NFPA 70E, a Standard for Electrical Safety in the Workplace, in 1979. This national consensus standard of electrical safety covers a variety of work practices, installation, maintenance and special equipment. It also outlines requirements to help keep workers safe from electrical arc-flash and flash fire. Highlights include:
Workers must wear appropriate flame resistant clothing (FRC) and personal protective equipment (PPE).
All equipment must be de-energized, except in unusual circumstances.
Where arc flash is a danger, employers must conduct flash hazard analysis and create a flash protection boundary.

NFPA 70E is the first standard to specifically require arc flash PPE while working on or near live power greater than 110 volts. After arc hazard levels have been assigned for job tasks, contractors can determine which types of PPE must be used.

Table 130.7 (c)(11) from NFPA 70E-2004 shows the Hazard Risk Category (HRC), a description of clothing appropriate for that category, and the corresponding Arc Thermal Performance Value (ATPV) ratings. Contractors can use this table to determine what level of protective clothing their workers must wear when arc flash dangers may be present.

HRC is defined as a rating range related to ATPV. There are five HRCs ranging from zero to four. Zero represents the least amount of risk to a worker, while four represents the greatest amount of risk.

ATPV is defined as a rating assigned to flame-resistant PPE that measures the amount of protection the clothing can provide. Heavier weight fabrics are generally assigned a higher ATPV. Workers wearing multiple layers of FRC can add the ATPVs of each garment to reach greater levels of protection.

NFPA 70E also states that contractors must de-energize all equipment before working on it unless the employer can demonstrate that de-energizing the equipment introduces additional or increased hazards. Equipment may also stay energized if it is not feasible to turn it off because of equipment design or operational limitations.

OSHA allows work on energized equipment in two instances:
1. Where continuity of service must be maintained. For example, contractors need to keep equipment energized to perform diagnostics or testing that can only be performed when the equipment is energized.

2. When de-energizing may create additional hazards such as interruption of life support equipment, shutdown of emergency alarm systems and shutdown of hazardous ventilation equipment.

In every other case, lockout/tag out is federal law. Convenience is not an acceptable excuse for keeping equipment energized.

Compliance with NFPA 70E is not mandatory. Instead, it is a national consensus safety standard published by NFPA to help OSHA create electrical safety standards. OSHA has yet to incorporate it into the Code of Federal Regulations.

However, OSHA can still cite contractors for not complying with NFPA 70E. It’s up to the employer to assess the workplace for electrical hazards and need for PPE. Compliance with 70E will assure compliance with OSHA’s PPE regulation 29 CFR 1910.335(a)(1)(i).

Flash hazard analysis
When contractors determine that electrically energized conductors pose a risk to workers of greater than or equal to 50 volts, and workers must conduct maintenance or service on the conductors while they are energized, NFPA 70E Article 130.3 requires contractors to conduct a flash hazard analysis.

The flash hazard analysis establishes a protected distance from exposed energized conductors, which a worker may receive a second-degree – or curable – burn, if arc-flash occurs.

Any worker inside this protective boundary must wear proper FR clothing. Typically, the flash protection boundary for equipment operating at 600 volts or less is 48" away from the equipment. Contractors can use NFPA’s Hazard Risk Category Classifications, or NFPA 70E Table 130.7 (c)(9)(a), to determine risk level and the right PPE.

Dress appropriately
Since the advent of NFPA 70E, many PPE suppliers have rolled out lines of protective clothing, including gloves, shirts, pants, boots, coveralls, face shields and more.

Manufacturers assign ATPV numbers to each garment to represent the amount of energy required to cause a second-degree burn through the garment. The number also represents the level of protection the garment provides in case it comes in contact with electrical arc.

However, flame resistant (FR) does not mean fire proof. “There’s a difference between FR and fire proof,” says John Mozena, Carhartt public relations manager. “Fire proof means that it won’t burn; these fabrics are used by firefighters and race car drivers. FR will burn as long as you hold a flame to the garment.”

FR clothing is designed to extinguish the flame in order to keep it from spreading. In Carhartt’s case, FR cotton is treated with phosphorous and nitrogen to make it flame resistant. These chemicals are not dangerous to the worker’s skin. The chemically treated cotton will self-extinguish the flame as soon as the ignition source is gone.

Carhartt also recommends taking a close look at ATPV and HRC, which basically measure how hot a particular fabric needs to get before it chars through. HRC is a simple way to break down the ATPV scale.
“The ATPV rating can be added together to reach compliance levels,” says Mozena. “We put a lot of effort into a variety of types of FR clothing. Contractors that need a 40 ATPV don’t need to solely use a 40 ATPV jacket. They can wear a 30 ATPV jacket and a 10 ATPV shirt and be just fine. However, HRC does not stack like ATPV.”

The right fit
Knowledge about FR clothing does no good unless the clothing protects workers when it’s supposed to. That can’t happen when a worker leaves his FR clothing in the truck because it doesn’t fit right, it’s too hot or it’s uncomfortable.

“We try very hard to convince contractors they don’t need to sacrifice functionality to get flame resistance,” says Mozena. “The safety officers we talk to say comfort equals compliance.”

“It’s one thing if you’re on a single-site construction area where the safety officer can look over everyone’s shoulder,” says Mozena. “It’s different if the safety officer can’t keep an eye on everyone. The best FR garment doesn’t do anything if the guys leave it in the truck because they’re not comfortable in it during a long day on the job.”

Published in the May/June 2008 issue of Contractor Tools and Supplies magazine.

back to top